The present invention relates to filter apparatus, and particularly to a self-cleaning filter which automatically cleans itself after it has accumulated a predetermined quantity of particles filtered from the fluid. The invention is particularly useful for filtering water irrigation systems and is therefore described below with respect to such an application, but it will be appreciated that the invention could advantageously be used in other applications as well.
Irrigation systems commonly include filters for removing foreign particles, for example sand or sediments, from the water in order to prevent clogging of the water irrigation devices, such as water sprinklers or drip emitters, connected to the water supply line. It is advantageous in such applications to have the filter clean itself periodically, as required, without either turning off the water, or detaching the filter from the water supply line.
Many disc filters are used to filter upstream water across a compressed stack of disc-like filtering elements. The disc-like filtering elements are stacked on a spine that facilitates aligning the disc stack. The compressed disc stack form a filtering element that traps sediments along the disc surface and/or along the external (upstream) surface of the stack of discs. In that way upstream water is filtered across the disc stack to produce downstream clean water.
One known way for self-cleaning such a disc filter in such applications is by reverse flushing. During back flushing process the reverse flow, downstream to upstream, is used to unstack the filtering elements and to flush out and therefore clean the filtering discs from any associated sediments. Part of the reverse flow stream is piped through the filter's spine into channels having multiple spray nozzles configured to produce a tangential flow through each nozzle. The tangential flow is used to clean the disc filtering elements across its surface. The tangential flow further causes the filtering disc elements to spin while filtered debris is flushed away from its filtering surface and toward the upstream inlet. In this manner the reverse flow is used for flushing the filtering elements from trapped debris allowing the filtering system to continuously work.
Usually such self-cleaning disc filters are utilized in a network of filters that are controlled with various valve control arrangements so that certain filters in the network are used during the normal filtering operation, but upon the accumulation of an undue amount of foreign material within the filter, causing increased pressure differential across the filter, which signals to valve controls, directing the flow of water through the filter network, to redirect the water to flow through other filters in the network while the dirtied filters are flushed by the reverse flow, as described.
The cleaning rate of such filtering networks are co-related to the quality of the water being filtered, however, the filtering networks, particularly the cleaning process, are not sufficiently efficient or optimized. Specifically the pressure differential required to trigger the cleaning process and the pressure at which the reverse flushing is effectively performed are not optimized in state of the art back-flushing disc filter networks.